This invention relates to a method and apparatus for disinfecting water, and more particularly to such an apparatus and method which employ ultraviolet light generated by a laser.
Ultraviolet light is a known disinfection agent for water. It has been typical in the past to provide a series of banks of ultraviolet light bulbs and to flow the water to be treated over the surfaces of the bulbs. There are a number of disadvantages to this approach. First, the intensity of the ultraviolet light varies with the distance from the surface of the bulbs. Therefore, the bulbs must either be very closely spaced or special bulb arrays must be used which provide sufficient intensity of the ultraviolet light for all water flowing past the bulbs. Even then, the flow past the bulbs must be relatively slow so that an adequate dosage of the ultraviolet light is likely to result. The close spacing of the bulbs results in considerable head loss. Secondly, the bulbs have a tendency to become coated or clouded thereby reducing the intensity of the ultraviolet light. One approach to overcoming this problem has been to provide apparatus which allows for periodic removal and cleaning of the bulbs so as to minimize the loss due to coating. A second approach to the coating problem has been to provide an ultraviolet light intensity which is greater than initially needed so that the intensity will still be adequate even after the bulbs become coated. Thirdly, bacteria which are supported by suspended particles may not be exposed to the ultraviolet light if it is shielded from the light source by the particle.
There are sources of ultraviolet light in addition to the bulbs or lamps now commonly used for disinfection. One source is a laser which, by proper selection of the lasing gas, can be caused to radiate light in the ultraviolet range. The use of laser generated ultraviolet light has not been heretofore proposed for the disinfection of wastewater. The laser has decided operating advantages, including the ability to have its intensity, controlled in relation to operating conditions, such as flow rate, or characteristics of the water or other fluid being treated, such as turbidity or organic content. The geometry of the beam is also controllable to adjust for changing in operating conditions or fluid characteristics. The laser is capable of generating high intensity ultraviolet light and allows for faster velocities of the water, reduces head loss, will tolerate higher turbidity in the water and reduce the possibility of bacteria not being exposed to the ultraviolet light.
I have found ways in which to efficiently and effectively utilize the laser in the disinfection of water. By disinfection is meant the ability of a laser radiating in the ultraviolet spectrum to kill bacteria primarily by direct contact rather than by secondary photochemical effects. While these secondary effects might have the effect of killing the bacteria they can also lead to a reactivation of the bacteria which will have a negative effect on the disinfection process. Although my method and apparatus is particularly adapted for the treatment of water, it can also be employed to disinfect fluids generally, including those which are water based and those which are not, and including gases such as air.